氧化物对3CaO·3Al2O3·CaSO4形成的影响

借助XRD测试手段研究了Al2O3、SiO2、Fe2O3以及MgO几种生料中常见氧化物对高温固硫物相3CaO·3Al2O3·CaSO4形成的影响.结果表明,改变Al2O3的含量,不会对3CaO·3Al2O3·CaSO4的形成产生明显影响;Fe2O3及MgO的存在能降低3CaO·3Al2O3·CaSO4的形成温度,但也使其分解温度提前;SiO2的大量存在则会抑制3CaO·3Al2O3·CaSO4的形成.     

MgO与Al2O3对Al-MgO-Al2O3体系中MgAlON形成机理的影响

以电熔镁砂、α-Al_2O_3微粉、板状刚玉、白刚玉、金属铝及高纯镁砂为原料,铝酸镁溶胶为结合剂,氮气条件下1 700℃保温4 h分别制备了MgO基和Al_2O_3基Al-MgO-Al_2O_3复合材料。研究了氮气低氧分压条件下MgO和Al_2O_3稳定性差异对Al-MgO-Al_2O_3复合材料微观结构的影响并揭示了MgO基和Al_2O_3基中MgAl ON形成机理。结果表明:在氮气低氧分压条件下,MgO比Al_2O_3更不稳定;在1 000℃以上随着温度的升高,体系MgO和Al_2O_3反应形成MgAl_2O_4,随着温度的升高,C-O_2反应的进行,体系内氧分压逐渐降低,MgO不稳定,分解为Mg(g)和O_2(g)。在MgO基体系中,MgO分解量较多,导致局部氧分压升高,金属Al部分将被氧化成Al_2O(g),与N_2(g),Mg(g)和O_2(g)发生反应,生成片状MgAl ON:Al_2O(g)+O_2(g)+N_2(g)+Mg(g)→MgAl ON(s)。而在Al_2O_3基体系中,由于MgO分解量减少,氧分压较低,高温下金属Al转变成Al(g),与N_2(g),Mg(g)和O_2(g)反生反应生成板片状MgAl ON:Al(g)+O_2(g)+N_2(g)+Mg(g)→MgAl ON(s)。     

Mg4.68Al2.64Zr1.68O12的合成机理

以分析纯的MgO、活性α-Al2O3、电熔单斜锆为原料,采用淬冷法研究了Mg5+x Al2.4–x Zr1.7+0.25x O12(–0.4≤x≤0.4)的化学组成、热处理温度对合成MgO–MgAl2O4–ZrO2系三元化合物的影响,并对其合成机理进行了分析。结果表明:当温度低于1 650℃时,主要为MgAl2O4的形成及其晶粒长大过程;当温度高于1 650℃时,MgO与ZrO2向MgAl2O4扩散,反应形成了Mg4.68Al2.64Zr1.68O12;当温度为1 740℃时,Mg4.68Al2.64Zr1.68O12的合成趋于完全,其合成率达到89.5%,残留的MgAl2O4和ZrO2主要分布在Mg4.68Al2.64Zr1.68O12晶内;在合成温度为1 760℃、x=–0.2条件下,Mg4.68Al2.64Zr1.68O12的合成率最大,高达89.99%,且其晶粒发育最为完善;Mg4.68Al2.64Zr1.68O12在低温下分解成MgO、MgAl2O4和C-ZrO2共析体,实现了MgAl2O4和ZrO2的高度分散。     

透明MgAl2O4晶须的制备与表征

本文采用MgO粉和金属Al粉为原料,在氮气气氛下制备MgAl2O4晶须,研究了TiO2、SiO2或Cr2O3等供氧添加剂和制备条件对晶须合成率的影响并分析了晶须的物相组成和结构.结果表明:最佳MgO/Al=2/3;添加SiO2或Cr2O3不利于晶须合成;添加TiO2对合成晶须有促进作用,最佳TiO2加入量为40%;采用氧化铝坩埚比采用釉面陶瓷坩埚好,最佳保温时间为6 h.合成的晶须为MgAl2O4,空间群Fd3M,晶格常数a=b=c=0.8083 nm,MgO 28.3%,Al2O3 71.7%;晶须呈透明柱状,最大长度为20～30 mm,长径比20～400.     

矿物3CaO·3AI2O3·BaSO4高温稳定性研究

矿物3CaO·3Al2O3·BaSO4是一种新型胶凝矿物, 而关于其高温稳定性的研究却有多种结论.本工作综合运用IR, TG-DT A,EPMA,XRD和QXDA等多种测试方法, 系统研究了3CaO·3Al2O3·BaSO4 的高温稳定性问题.研究表明, 在温度低于1 350 ℃的条件下, 矿物3CaO·3Al2O3·BaSO4的晶相结构稳定; 而温度高于1 360 ℃时, 3CaO·3Al2O3·BaSO 4发生分解并形成新的晶相.3CaO·3Al2O3·BaSO4的分解方程式可表述为: 3CaO·3Al2O3·BaSO4→CaO·Al2O3+12CaO·7Al2O3+Ba O·Al2O3+SO2↑+O2↑鉴于矿物BaO·Al2O3的形成机理与该问题紧密相关, 本文也讨论了BaO·Al2 O3的形成机理.BaO·Al2O3的形成机理有两种:温度低于1 350 ℃时, BaO·Al2O 3由原料组分发生反应而形成的; 而温度大于1 360 ℃时, 该矿物是由3CaO·3Al2O 3·BaSO4分解形成的.     

气氛和碳对MgO-C耐火材料基质中原位尖晶石形成的影响

碳、空气和还原气氛对MgO—C耐火材料基质中原位MgAl2O4尖晶石的形成在显微结构和相分析方面的影响，可由X射线衍射分析和扫描电子显微镜分析／能谱分析得到研究。尖晶石形成于1000℃以下的空气和还原气氛中。原位尖晶石的形态和它的形成机理的不同受气氛的影响。一般认为在氧化气氛中固态反应是尖晶石形成的主要机理，发现气-固反应在还原气氛中发挥关键作用。在还原气氛中MgO和C反应而生成Mg（气），在还原气氛下烧成形成原位尖晶石。重点解释了其在MgO—C耐火材料中的应用。     

AlON的氧化行为及其与MgO和MgAl2O4的作用

利用TG DTA和XRD研究了氧氮化铝(AlON )在高温下的氧化行为及其与MgO和MgAl2 O4 的作用。结果表明 :AlON在 85 0℃左右开始氧化 ,1170℃左右氧化最为剧烈 ;MgO和MgAl2 O4 在 12 0 0℃都能与AlON形成固溶体 ,且后者更易形成 ;形成固溶体对AlON的氧化有一定的抑制作用。     

KCl-LiCl-KF系熔盐介质中MgAl_2O_4粉体的合成制备

以工业氧化铝和轻质氧化镁(分析纯)为主要原料,在500~1 000℃范围内,研究了KCl、LiCl及KCl-LiCl熔盐介质中MgAl2O4粉体的合成制备以及KF的作用和影响。采用X射线衍射仪、激光粒度分析仪及扫描电子显微镜对产物粉体进行了分析表征,并探讨了MgAl2O4的合成反应机制。结果表明:1)复合熔盐(KCl-LiCl)较之单一熔盐(LiCl、KCl)、单一熔盐LiCl较之KCl更有利于MgAl2O4粉体的合成;2)KF的引入能促进熔盐介质中MgAl2O4的形成,并明显降低MgAl2O4的合成温度;3)在未引入KF的熔盐介质中,MgAl2O4合成反应机制为模板机制;在引入KF的熔盐介质中,MgAl2O4合成反应机制包括模板机制和溶解-沉淀机制。     

堇青石陶瓷烧结工艺及机理研究

本文利用DSC、XRD技术，研究了MgO、Al2O3，和SiO2反应烧结制备堇青石陶瓷的机理。结果表明MgO和Al2O3在1155℃反应合成镁铝尖晶石(MgAl2O4)，进而在1317℃长时间保温与SiO2反应生成堇青石。     

NT705型脱硫剂的本征动力学研究

用热重法研究了还原后的NT70 5型脱硫剂脱除合成气中H2 S的脱硫反应本征动力学。在很强的还原氛围中 ,4 0 0℃的条件下 ,脱硫剂中的Fe2 O3 被还原为Fe3 O4,并进一步还原为FeO ,最终还原为单质Fe。实验采用 10 0 12 0目的小颗粒 ,在 2 80 4 0 0℃范围内 ,原料气H2 S质量浓度为 0 995 5 2 g/m3 的条件下进行。实验数据用未反应收缩核模型处理 ,结果表明 ,小颗粒脱硫剂的脱硫反应速率为化学反应控制 ,脱硫反应为一级反应     

Reactions Between Alkaline-Earth Sulfates and Cirstobalite

The decomposition of magnesium and calcium sulfates was measured preliminary to measuring the reactions between alkaline-earth sulfates and cristobalite. Since gaseous sulfur oxides were evolved in the processes, a starch-iodide titration was used to determine the amounts of decomposition and reaction with time. Magnesium sulfate decomposed at temperatures above 900°C, before reaction with cristobalite. Calcium sulfate was found to react with cristobalite previous to thermal decomposition with an accompanying evolution of sulfur dioxide. Strontium and barium sulfates reacted with cristobalite at progressively higher temperatures. The applications of the data to the sulfur problems in the production of clay products are discussed.     

Mechanism for environmental etch of acrylic melamine-based automotive clearcoats: Identification of degradation products

This paper focuses on defining the reaction mechanism involved in the environmental etch of acrylic melamine-based automotive clearcoats via an identification of reaction products. This has been accomplished through a comparative study of products formed on acid treatment of neat crosslinkers, and those formed following laboratory acid treatment and field exposure of acrylic melamine clearcoat systems. Bulk elemental, X-ray photoelectron spectroscopy (XPS), and infrared (IR) analyses of sulfuric acid-treated melamine crosslinkers show that acid hydrolysis results primarily in the formation of melamine sulfate. Melamine sulfate formation was also observed following laboratory and field exposure of acrylic melamine clearcoat systems. These results confirm that the primary mode of melamine crosslink decomposition is through hydrolysis of acetal linkages and subsequent formation of melamine sulfates. However, data show that hydrolysis of pendent amino groups on the triazine ring also occurs. Ford Research Laboratory, P.O. Box 2053, MD 3083 SRL, Dearborn MI 48121. E-mail: pschmit1@ford.com     

Advances and gaps in the knowledge of thermodynamics and crystallography of acid mine drainage sulfate minerals

Acidic and metal-rich waters produced by sulfide decomposition at mining sites are termed acid mine drainage (AMD). They precipitate a number of minerals, very often sulfates. The recent advances in thermodynamic properties and crystallography of these sulfates are reviewed here. There is a reasonable amount of data for the divalent (Mg, Ni, Co, Fe(2+), Cu, Zn) sulfates and these data may be combined with and optimized by temperature-relative humidity brackets available in the literature. For the sulfates with Fe(3+), most data exist for jarosite; for other minerals and phases in this system, a few calorimetric studies were reported. No data whatsoever are available for the Fe(2+)-Fe(3+) sulfates. A significant advance is the development of the Pitzer model for Fe(3+)sulfate solutions and its confrontation with the available thermodynamic and solubility data. In summary, our knowledge about the thermodynamic properties of the AMD sulfates is unsatisfactory and fragmented.     

Study of chloride binding and diffusion in GGBS concrete

Ordinary Portland cement (OPC) and OPC/ground granulated blastfurnace slag (GGBS) 70%, with or without 5% sulfates, were widely investigated in respect to their pore structures, chloride diffusion coefficients, internal and external chloride-binding capabilities by expression method and leaching method and the microstructure analysis on Friedel's salt such as differential thermal analysis (DTA), X-ray diffraction (XRD) and scanning electron microscopy (SEM). It can be concluded that GGBS can improve the pore structure of OPC and decrease the chloride diffusion coefficient greatly, and that sulfates do not do good for the pore structure and chloride diffusion for GGBS. GGBS increases the chloride-binding capability greatly without reference to the internal or external chloride and sulfates decrease the chloride-binding capability of GGBS greatly. It can be also found that the maximum intensity peak corresponding to Friedel's salt appears at about 8.0 Å, its endothermic effect appears at about 360 °C, its morphology is hexagonal slice whose size is about 2-3 μm; that the output of Friedel's salt formed by GGBS is much more than OPC; and that sulfates influence the output of Friedel's salt greatly. The corresponding mechanism was also analyzed.     

Decomposition of CCl2F2 over metal sulfate catalysts

Activity for hydrolysis of CCl₂F₂ (CFC12) on various metal sulfate was investigated. Zr(SO₄)₂ was found to be the most active while FeSO₄, Cr₂(SO₄)₃, Al₂(SO₄)₃, La₂(SO₄)₃ and Ce₂(SO₄)₃ had intermediate activity. MnSO₄, CoSO₄, and MgSO₄ showed low activity and SrSO₄, CaSO₄, and BaSO₄ had even less activity. The major carbon containing product was CO₂ and small amount of CClF₃ and CO were formed over several sulfates. The crystal structure of the sulfates was stable during decomposition of CCl₂F₂, and the conversion reached a steady state after initial decrease at 275 °C over Zr(SO₄)₂ catalyst. The concentration of surface hydroxyl was larger than that over AlPO₄-based catalysts and a reaction mechanism similar to that over AlPO₄-based catalysts was proposed.     

CRITICAL STUDY OF METHODS OF DETERMINING EXCHANGEABLE BASES IN CLAYS *

A study was made of analytical methods of determining exchangeable bases in clays and similar ceramic materials. Total exchange capacity can be determined by electrodialysis or by the teaching-distillation method. The time required for electrodialysis can be materially reduced by agitation of the clay slip during dialysis. Electrodialysis effects decomposition of bentonite and similar materials unless extremely low current densities are applied. Exchangeable cations of clays and similar materials are replaced slowly by percolation methods, but an agitation leaching-centrifuging procedure was developed which effects a rapid replacement. In ultimate analyses by leaching methods, correction must be made for soluble sulfates. Aqueous 1 N ammonium acetate is a satisfactory leaching solvent for most clay bodies, but for those containing appreciable amounts of calcium carbonate, alcoholic ammonium acetate should be employed. Details of recommended analytical procedures are given.     

SCR脱硝中催化剂表面NH4HSO4生成及分解的原位红外研究

采用工业用V₂O₅-WO₃/TiO₂催化剂,基于傅里叶原位红外光谱(in situ FT-IR)技术考察了SCR脱硝过程中催化剂表面NH₄HSO₄的生成与分解特性。结果表明:在V₂O₅-WO₃/TiO₂催化剂表面ABS的生成可由催化剂V═O基团上Lewis酸上配位吸附活化态的NH₃在O₂环境中与SO₂反应生成,也可由SO₂与催化剂表面反应生成的吸附态金属硫酸盐中间物VOSO₄与气态NH₃直接反应生成;NO能通过与NH₄HSO₄中的NH₄⁺直接反应来降低NH₄HSO₄降解的温度窗口,促进其在催化剂表面的分解行为,NO的脱除与NH₄HSO₄的生成是相互抑制关系;NH₄HSO₄本身的负载量影响其分解与挥发行为。     

MgO与ZrSiO_4反应烧结机理研究

应用ＳＥＭ方法观察了ＭｇＯ与ＺｒＳｉＯ_４的反应烧结机理。结果表明,随着ＺｒｓｉＯ_４的分解,ＳｉＯ_２呈不定形态向外扩散,与ＭｇＯ反应生成Ｍｇ_２ＳｉＯ_４,原来的锆英石颗粒中只留下了ＺｒＯ_２,同时ＭｇＯ向ＺｒＯ_２方向移动,与ＺｒＯ_２形成有限固溶体;反应产物之一ＺｒＯ_２大部分聚集成集合体,也有一部分分布比较均匀。     

Does pyrite oxidation contribute to the acidification of tropical peat? A case studyin a peat swamp forestin Central Kalimantan,Indonesia

The chemical properties of peat pore water in the basin of the Sebangau River and Lahei district, Central Kalimantan, Indonesia, were studied. We analyzed major ions, pH, electrical conductivity (EC) and redox potential (Eh) of the peat pore water with reference to their vertical profile. We evaluated the contribution of sulfates to the acidi.cation of peat by including data from Furen mire, eastern Hokkaido, Japan. The coastal peat of Furen mire and the peat in Paduran in the lower basin of the Sebangau River included extraordinarily high concentrations of sulfates (> 1000 mg/l) compared to the peat in the middle and upper basins of the river (< 10 mg/l). High concentrations of sulfates, however, did not lead to a low pH for the peat. The present findings suggest that the acidification of the peat pore water is subject to the production of organic acids originating from peat decomposition, rather than the production of sulfuric acid produced by pyrite oxidation in the underlying mineral sediments.     

Characterization of Freeze-Dried Al2O3 and Fe2O3

Oxide crystallite formation and growth from freeze-dried sulfates were studied for the representative materials Al₂O₃ and Fe₂O₃. Transmission and scanning electron micrographs showed the formation and growth of chainlike aggregates of crystallites. Aggregation occurred as part of the nucleation and growth of the oxide, and discrete oxide particles were never present. Orientation of the chain aggregates was related to the ice structure formed during freezing. X-ray line broadening data showed that crystallite size is a function of the 1/5 to 1/7 power of time for isothermal treatments. A qualitative analysis of material transport favored the surface diffusion mechanism.